An exemplary embodiment of this invention relates to optical printed circuit board technology, and particularly to methods for passive alignment of adapters, enabling high-precision connection between optical flexes and optical elements in which the methods are based on removable reference structures.
Currently, numerous worldwide industrial and academic R&D teams are working on the development of an optical printed circuit board (PCB) technology. One of the hurdles of this development is to find a reliable, high-precision, low-cost method to align components, such as optical connectors, vertical cavity surface emitting laser (VCSELs), photodiodes, and lenses on the PCB.
However, the described alignment issue for optical PCBs can also be understood in a much broader sense and can be transferred to other fields of application where a high-precision, fully passive, mechanical alignment of components on a low-precision carrier is required.
With regard to optical PCB development, the major challenge of the mentioned alignment task lies in the fact that for conventional PCBs, he manufacturing tolerances (e.g., board distortion tolerances, copper layer patterning tolerances, mutual layer alignment tolerances, milling tolerances) are typically 100 μm (micrometers), while for multi-mode optical links on optical PCBs, the alignment tolerances to achieve sufficient optical coupling efficiency between optical components are about 5 μm.
In order to address this discrepancy between PCB and optical requirements, most of the solution approaches worldwide are based on actively controlled, time-consuming, and therefore cost-intensive alignment procedures. FIG. 1 illustrates an example of a fully passive alignment method. In the passive alignment method, alignment structures 110 (e.g., a set of copper alignment markers) integrated in the PCB 120 and realized by conventional PCB processes take manufacturing tolerances into account. These cooper alignment structures 110 serve as reference markers to find back the position of the integrated waveguides (not shown) patterned with respect to the copper alignment structures 110. Furthermore, these copper alignment structures 110 exhibit mechanical features for the alignment and assembly of mechanical adapters 130 carrying the component to be aligned. Finally, the placement of the adapter 130 onto the PCB 120 can be performed by a low-precision handling tool 140 or by a conventional pick-and-place tool. Further details of a passive alignment method may be found, for example, in U.S. Pat. No. 7,212,698, herein incorporated by reference.
For many alignment tasks within the field of optical PCBs, the above-described method will be fully sufficient. However, there may be certain applications where the footprint of the copper markers (e.g., copper alignment structures 110) and the dimensions of the adapter 130 could be an issue in terms of the space requirments at a PCB edge or within a PCB. The board edge can become a bottleneck regrading the available space for the required electrical as well as optical connectors. A similar situation can occur within the board where board openings are realized for the assembly of components, such as optical transceiver modules.
In both cases, it would be beneficial to have methods to reduce the footprint of the marker set and the adapter and to have more freedom in the positioning and the design of these features. Further, it would be beneficial to use these features for the alignment of the component and to make them removable to retrieve the space required by the alignment features.